ZHCSIX0H March   2009  – October 2018 LM5008A

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
    1.     Device Images
      1.      典型应用，基本降压稳压器
  4. 4 修订历史记录
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Control Circuit Overview
      2. 7.3.2 Start-Up Regulator (VCC)
      3. 7.3.3 Regulation Comparator
      4. 7.3.4 Overvoltage Comparator
      5. 7.3.5 On-Time Generator and Shutdown
      6. 7.3.6 Current Limit
      7. 7.3.7 N-Channel Buck Switch and Driver
      8. 7.3.8 Thermal Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Active Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Custom Design With WEBENCH® Tools
        2. 8.2.2.2 Selection Of External Components
        3. 8.2.2.3 Low-Output Ripple Configurations
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11器件和文档支持
    1. 11.1 器件支持
      1. 11.1.1 第三方产品免责声明
      2. 11.1.2 使用 WEBENCH® 工具创建定制设计
      3. 11.1.3 开发支持
    2. 11.2 文档支持
      1. 11.2.1 相关文档
        1. 11.2.1.1 PCB 布局资源
        2. 11.2.1.2 热设计资源
    3. 11.3 接收文档更新通知
    4. 11.4 社区资源
    5. 11.5 商标
    6. 11.6 静电放电警告
    7. 11.7 术语表
  12. 12机械、封装和可订购信息

封装选项

机械数据 (封装 | 引脚)
散热焊盘机械数据 (封装 | 引脚)
订购信息

7.3.2 Start-Up Regulator (VCC)

The high voltage bias regulator is integrated within the LM5008A. The input pin (VIN) can be connected directly to line voltages between 6 V and 95 V, with transient capability to 100 V. Referring to the Functional Block Diagram and Figure 2, when VIN is between 6 V and the bypass threshold (nominally 8.5 V), the bypass switch (Q2) is on, and VCC tracks VIN within 100 mV to 150 mV. The bypass switch on-resistance is approximately 100 Ω, with inherent current limiting at approximately 100 mA. When VIN is above the bypass threshold Q2 is turned off, and VCC is regulated at 7 V. The VCC regulator output current is limited at approximately 9.2 mA. When the LM5008A is shut down using the RT/SD pin, the VCC bypass switch is shut off regardless of the voltage at VIN.

When VIN exceeds the bypass threshold, the time required for Q2 to shut off is approximately 2 µs to 3 µs. The capacitor at VCC (C3) must be a minimum of 0.47 µF to prevent the voltage at VCC from rising above its absolute maximum rating in response to a step input applied at VIN. C3 must be placed as close as possible to the VCC and RTN pins. In applications with a relatively high input voltage, power dissipation in the bias regulator is a concern. An auxiliary voltage of between 7.5 V and 14 V can be diode connected to the VCC pin to shut off the VCC regulator, thereby reducing internal power dissipation. The current required into the VCC pin is shown in Figure 6. Internally a diode connects VCC to VIN requiring that the auxiliary voltage be less than VIN.

The turnon sequence is shown in Figure 8. During the initial delay (t1), VCC ramps up at a rate determined by its current limit and C3 while internal circuitry stabilizes. When VCC reaches the upper threshold of its undervoltage lockout (UVLO, typically 5.3 V), the buck switch is enabled. The inductor current increases to the current limit threshold (ILIM), and during t2 the VOUT increases as the output capacitor charges up. When VOUT reaches the intended voltage the average inductor current decreases (t3) to the nominal load current (IO).

LM5008A 30074914.gifFigure 8. Start-Up Sequence